Method and apparatus for inspecting pattern defects

ABSTRACT

A method and apparatus for inspecting pattern defects emitting a laser beam, adjusting a light-amount of the laser beam, converting the light-amount adjusted laser beam into a slit-like laser light flux, lowering coherency of the slit-like laser light flux, and irradiating a sample with the coherence reduced slit-like laser light flux. An image of reflection light from the sample is obtained, and a detector is provided which includes the image sensor for receiving the image of the reflection light and for converting it into a detected image signal. An image processor is provided for detecting defects on patterns formed on the sample in accordance with the detected image signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 11/192,021, filed Jul. 29, 2005, now U.S. Pat. No. 7,110,105, whichis a continuation application of U.S. application Ser. No. 10/218,463,filed on Aug. 15, 2002, now U.S. Pat. No. 6,927,847, the contents ofwhich are incorporated by reference, and is related to U.S. applicationSer. No. 10/650,756, filed Aug. 29, 2003, now U.S. Pat. No. 6,900,888,and U.S. application Ser. No. 11/131,379, filed May 18, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to inspection of patterns and/or foreignmatters, for detecting or examining defects, such as short-circuitand/or open-circuit or the like, on the patterns as a target ofinspection, and relates, in particular, to a method and an apparatus,for inspecting the defects and/or foreign matters of the patterns formedon, such as, a semiconductor wafer, a liquid crystal display, and aphoto-mask, etc., for example. Hereinafter, it is assumed that thedefects include the foreign matters, in the meaning thereof.

Conventionally, in such kind of an inspection apparatus, as is describedin Japanese Patent Laying-Open No. Hei 7-318326 (1995) <hereinafter,conventional art 1>, an image is detected on the patterns to be examinedor inspected by means of an image pick-up element, such as a linesensor, etc., while moving the patterns to be inspected, so as tocompare an image signal detected with one which is delayed by apredetermined time in gradation thereof, thereby acknowledginginconsistency or anti-coincident to be a defect.

Also, other conventional art, relating to the defect inspection ofpatterns to be inspected, is known from Japanese Patent Laying-Open No.Hei 8-320294 (1996) <hereinafter, conventional art 2>. In thisconventional art 2 is described a technology, for examining the patternsto be inspected, for example, a semiconductor wafer, in which areas highpattern density, such as the memory mat portions, etc., and low patterndensity, such as peripheral circuit portions, etc., are mixed with eachother, wherein gradation conversion is conducted on digital image orvideo signal, which is obtained through A/D conversion of the imagesignal detected, so that a predetermined relationship can be establishedbetween the high density areas and the low density areas on the patternsto be inspected, in particular in the brightness or the contrastthereof, rather than the frequency distribution thereof, and this imagesignal converted in gradation is compared with other gradationconversion image signal for comparison, under the condition of beingfitted to each other in position, thereby inspecting minute ormicroscopic defects thereon with high accuracy.

Furthermore, the conventional art for inspecting the patterns on aphotomask is already known, for example, Japanese Patent Laying-Open No.Hei 10-78668 (1998) <hereinafter, conventional art 3>. In thisconventional art, it is described that the UV light rays are irradiatedupon the mask, equally, in which coherence is lowered by rotating adiffuser panel inserted within an optical path, with using a UV laserbeam as a light source, such as, an excimer laser or the like, so as tocalculate out a characteristic amount or quantity from the obtainedimage data of the mask, thereby deciding or examining good or bad, i.e.,the quality thereof. And, a projection exposure apparatus with using anexcimer laser therein is already known, for example, in Japanese PatentLaying-Open No. Sho 59-226317 (1964) or Japanese Patent Laying-Open No.Sho 62-231924 (1987), etc.

For LSI manufacturing in recent years, the circuit patterns formed on awafer come to be minimized, such as, 0.25 μm or less than that in thepattern width thereof, responding to the needs of high integration; thusit nearly reaches up to the limit on the resolving power of animage-forming optical system. For this reason, development is advancedon application of high NA technology or an optical super resolving powertechnology.

However, the NA technology also reaches up to the limit thereof,physically. Accordingly, a substantial or intrinsic approach is tryingto shift the light wavelengths to be applied for the detection into theregions of the UV light and DUV light, i.e., shortening the lightwavelength.

Further, due to the necessity of conducting the inspection with highspeed, it is impossible to adopt the method of scanning the laser beamfocused or converged thinly on a sample. On the contrary, when trying toilluminate with irradiating the laser beam spreading out all over avisual field, however the illumination of the laser beam generatesspeckles, or an overshoot or an undershoot, being called by a“wringing”, at an edge portion of the circuit pattern, thereby bringingabout a problem that the image cannot be obtained of good quality.

SUMMARY OF THE INVENTION

An object, according to the present invention, for dissolving such thedrawbacks of the conventional arts mentioned above, is to provided amethod and an apparatus, for inspecting or examining the microscopiccircuit patterns with high resolving power at high speed, therebyachieving inspection of the defects.

Also, other object, according to the present invention, is to provide amanufacturing method of semiconductor devices, with applying the methodand the apparatus for inspecting the pattern defects mentioned above,thereby enabling the manufacture of the super microscopic semiconductordevices.

According to the present invention, in a pattern defects inspectingapparatus using a UV light source or a UV laser beam source as a lightsource, being provided with a light-amount adjustment optical system foradjusting a light-amount of the UV light or the UV laser beam and acoherence reduction optical system for suppressing generation ofspeckles of the UV light or the UV laser beam, in an optical paththereof, wherein the UV light lowered in coherency is irradiated uponthe surface of a target, thereby detecting an image of the target to beinspected. Herein, the UV light includes a DUV light therein.

Namely, according to the present invention, a pattern defects inspectingapparatus is constructed with providing an illumination optical system,comprising: a light source for emitting a UV light, a laser light, or aUV laser light, etc.; a light-amount adjustment optical system foradjusting an light-amount of the UV light, the laser light, or the UVlaser light; a slit-like light flux optical system for forming the UVlight, the laser light, or the UV laser light into a slit-like lightflux for fitting to a light receiving portion, such as a TDI imagesensor, or the like; and a coherence reduction optical system forlowering coherency of the UV light, the laser light, or the UV laserlight, emitting from the slit-like light flux optical system, andfurther being provided with a detection optical system, having an imagesensor for detecting a detected image signal by picking up an image ofreflection light from the sample irradiated by the illumination opticalsystem, and an image processing portion for detecting the defects on thepatterns formed on the sample upon the basis of information relating tothe image signal of the sample detected by the detection optical system.

Also, according to the present invention, in the pattern defectsinspecting apparatus mentioned above, it is characterized that as animage sensor of the detection optical system is applied an image sensorof time delay integrated (TDI) type having a sensitivity to the UVlight.

And also, it is characterized that the image sensor of the time delayintegrated (TDI) type is an anti-blooming TDI sensor, a surfaceirradiation type TDI sensor, in which an organic thin-film coating istreated on a cover glass thereof, or a reverse surface irradiation typeTDI sensor.

Also, according to the present invention, there is provided a method forinspecting defects on pattern formed on a sample, comprising thefollowing steps of: irradiating the UV laser light lowered in coherencythereof upon surface of a sample; obtaining an image signal by pickingup an image of the surface of the sample irradiated by the UV laserlight; detecting defects on the sample, being equal or less than 10 nmin size, by processing the image signal; and outputting informationrelating to position on the sample with respect to the detected defectsbeing equal or less than 100 nm in size.

Further, according to the present invention, there is provided a methodfor inspecting defects, comprising the following steps of: irradiatingthe UV laser light lowered in coherency thereof upon a wafer having adiameter of 200 mm; detecting an image of the wafer by picking up animage of the wafer irradiated with the UV laser light; and detectingdefects on patterns formed on the wafer, being equal or less than 100nm, by processing the detected image of the wafer at throughput of equalor greater than three (3) pieces per an hour.

And also, according to the present invention, in the method forinspecting pattern defects, on the sample are formed with patternshaving repetitiveness.

Those and other objects, features and advantages of the presentinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for showing the structure of an apparatus forinspecting pattern defects on patterns to be inspected, according to anembodiment of the present invention;

FIGS. 2( a) and 2(b) are views for showing illumination conditions on apupil and a visual field of an objective lens for detection, under theillumination by means of a discharge tube;

FIGS. 3( a) to 3(d) are views for showing illumination conditions on apupil and a visual field of an objective lens for detection, a patternon the visual field and a signal detected therefrom, but under theillumination by means of laser radiation;

FIGS. 4( a) and 4(b) are views for showing illumination conditions on apupil and a visual field of an objective lens for detection, under theillumination by means of laser radiation, being widened or spread on thepupil thereof;

FIGS. 5( a) to 5(d) are views for showing illumination conditions on apupil and a visual field of an objective lens for detection, under theillumination by means of laser radiation according to the presentinvention;

FIG. 6 is a view for showing a relationship between a CCD detector andan illumination area on the visual filed, according to the presentinvention;

FIG. 7 is also a view for showing a relationship between a CCD detectorand an illumination area on the visual filed, according to the presentinvention;

FIGS. 8( a) and 8(b) are views for showing a relationship in anattachment of a laser beam source, according to the present invention;

FIGS. 9( a) and 9(b) are views for showing a adjustment manner in theattachment of the laser beam source, according to the present invention;

FIG. 10 is a view for showing a manner for adjusting an amount oflights, according to the present invention;

FIG. 11 is a view for showing a characteristic curve of an adjuster oflight amount, according to the present invention;

FIGS. 12( a) to 12(d) are views for explanation about an idea ofexchanging the illumination area or region, according to the presentinvention;

FIG. 13 is a view for explanation about an idea of forming theillumination area when inspecting, according to the present invention;

FIGS. 14( a) and 14(b) are views for explanation on an aperturediaphragm or stop, according to the present invention;

FIG. 15 is a view for explanation about an idea for lowering spatialcoherence of the illumination by laser radiation, according to thepresent invention;

FIGS. 16( a) to 16(c) are also views for explanation about the idea forlowering spatial coherence of the illumination by laser radiation,according to the present invention;

FIG. 17 is also a view for explanation about the idea for loweringspatial coherence of the illumination by laser radiation, according tothe present invention;

FIGS. 18( a) to 18 (c) are views for explanation about a second idea forlowering spatial coherence of the illumination by laser radiation,according to the present invention;

FIG. 19 is a view for explanation about an exchanging mechanism of anoptical path in a detector, according to the present invention;

FIG. 20 is a view for explanation about the mechanism of a image-forminglens, according to the present invention;

FIG. 21 is a view for explanation on a TDI image sensor, according tothe present invention;

FIG. 22 is also a view for explanation on the TDI image sensor,according to the present invention;

FIG. 23 is also a view for explanation about the characteristic curve ofthe TDI image sensor, according to the present invention;

FIG. 24 is a view for explanation on another TDI image sensor, accordingto the present invention;

FIG. 25 is a view for explanation about attachment of the TDI imagesensor, according to the present invention;

FIG. 26 is a view for explanation about an image filter in the imageprocessing, according to the present invention; and

FIG. 27 is a view for explanation about the image filter in the imageprocessing, according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments, i.e., a method and an apparatus for inspectingdefects on patterns to be tested, according to the present inventionwill be fully explained by referring to the attached drawings. FIG. 1 isa view for showing an embodiment of the apparatus according to thepresent invention. A stage 2 is built up with X, Y, Z and θ (rotation)stages, and this stage 2 is mounted a pattern to be tested or examined,such as, a semiconductor water (sample) 1, for an example. Anillumination light source 3 is built up with, such as, a UV laser beamsource irradiating the laser beam having wavelength of 266 nm or 355 nmtherefrom, i.e., it is a light source for illumination of a sample 1. Assuch the UV laser beam source, it may be built up with a device ofgenerating a third high-harmonic (355 nm) or a fourth high-harmonic (266nm) of a basic wavelength, in which a laser beam from a solid YAG laseris converted in the wavelength thereof through a non-linear opticalcrystal, etc. Or, it may be possible to adopt a laser beam source havingthe wavelength of 193 nm, or 248 nm. If being available as such the UVlaser beam source, it is also possible to adopt one having wavelength of100 nm or less than that, thereby improving the resolution much more.Further, it does not matter if the laser is in continuous oscillation orin pulse oscillation in the oscillation mode thereof, however inrelation with a fact that an image is detected from an object 1 to betested while driving the stage continuously, the continuous oscillationis preferable.

A light flux L1 from the laser beam source 3 is reflected upon a mirror4, which is rotated around an optical axis at a desired position, and islimited or restricted in an amount, down to that necessary forinspection, by means of a ND filter (an adjustment optical system forlight amount) 5 for restricting the amount of lights. The UV laser lightis expanded to a certain size of light flux by means of a beam expander6.

An optical system for exchanging optical illumination light path (anoptical system for exchanging illumination area) 7 is used for settingthe area of illumination upon the sample 1, exchanging between wheninspecting and when adjusting an inclination. Thus, the optical systemfor exchanging optical illumination light path (the optical system forexchanging illumination area) 7 exchanges the illumination area, so thatan illumination is made on a rectangle area or region (i.e., a slit-likearea) 71 covering an image sensor 51 when inspecting, while it is madeall over a detection area of a detector 18 when adjusting theinclination. However, when inspecting, in the optical system 7 forexchanging optical illumination light path, an aperture diaphragm 8 isset at a conjugate point with a pupil 14 a of an objective lens 14,thereby functioning to restrict the NA incident upon the pupil 14 a.Through a lens 9, the laser beam is guided to an optical system 10 forlowering coherence.

The coherence lowering optical system 10 is provided for lowering thecoherence of the laser beam emitted from the illumination light source3. This coherence lowering optical system 10 may be a one, which canlower the time or the spatial coherence. As such the coherence loweringoptical system 10, for example, it may be built up with a mechanism forscanning the laser beam from the illumination light source 3 on thepupil of the objective lens 14. An image of the laser beam from thecoherence lowering optical system 10 is formed on the pupil 14 a of theobjective lens 14 through a lens 11.

A beam splitter 12 may be constructed with a polarization beam splitterin a case, and is constructed, so that the UV illumination light fromthe UV illumination light source 3 reflects thereupon, to be given uponthe sample 1 through the objective lens 14, thereby giving abright-field illumination thereupon, for example. When the beam splitter14 is constructed with the polarization beam splitter, it has a functionof reflecting the UV laser beam thereupon if the polarization directionof the UV laser beam is in parallel with the reflection surface, whilepassing it therethrough if the polarization direction is perpendicularto the reflection surface. Accordingly, since the UV laser beam isinherently a polarized light, it is possible to bring about totalreflection of the UV laser beam, by means of the polarization beamsplitter 14.

A group 13 of polarization elements has a function of adjusting a ratiopf polarizing of the illumination light arbitrarily, through controllingthe polarization directions of the UV laser illumination light and thereflection light, so that the reflection light will not reach to animage sensor 20 with accompanying a blur or unevenness in brightness,due to the shape of pattern and/or the difference in density, and it maybe constructed with a ½ wavelength plate and a ¼ wavelength plate, forexample.

And, a beam splitter 16 and a lens 17, as well as, the detector 20,which are provided in the optical path defined between the beam splitter12 and the image sensor 20, are so constructed, that an image with awide visual field can be obtained by means thereof. Thus, when adjustingthe inclination of the sample, the wide field image of the sample 1 isformed on the detector 18 by means of the lens 17, for enablingobservation (picking-up of pictures) of the wide field image thereof.

Also, by means of an image-forming lens 19 is formed an image of thereflection light on the image sensor 20, which is detected by theobjective lens 14. Insertion of a mirror 21, which can be inserted, onthe optical path between the image-forming lens 19 and the image sensor20 enables an image-forming of the sample 1 on the detector 22, beingsame to that formed on the image sensor 20.

In this manner, by setting a rotation angle of the ½ wavelength plateand the ¼ wavelength plate, respectively, with rotating them around theoptical axes thereof, upon the basis of the spatial image formed on thepupil surface, which is detected from the detector 18, a CPU (not shownin the figure) controls the polarization condition of the reflectionlight generated from the circuit patterns formed on a semiconductorwafer 1, i.e., the diffraction light in the reflection light; therefore,it is possible to detect the image, for example, with reducing thediffraction light of 0^(th) order but hardly reducing diffraction lightsof other higher orders, by means of the image sensor 20. As a result,the image of the patterns can be improved progressively in the contrast,and thereby stable detection sensitivity can be obtained. However, forthe purpose of observation (picking-up of the pictures) of the spatialimage on the pupil surface 14 a of the objective lens 14 by means of thedetector 18, it is necessary to replace the lens 17 with a lens or thelike, which can form the spatial image on the pupil 14 a on the detector18.

As the objective lens 14, because of adoption of the UV light or the DUVlight therein, it is possible to lessen an ill influence due tochromatic aberration by using a reflection objective lens. Also, whenirradiating the UV light upon the sample, as the objective lens 14 isused one having the NA greater than 0.75.

The image sensor 20 has pixels, each being from 0.05 μm to 0.3 μm in thesize, converted onto the sample, and providing an output of an imagesignal of density (or gradation) depending upon the brightness(gradation) of the reflection light from the semiconductor wafer 1, asone example of the patterns to be inspected. However, those opticalsystems are expanded on an optical frame or base not shown in thefigure, and are constructed with the laser and the illumination opticalsystem, the detection optical system, and the sensors, in one body. Theoptical base is provided on an upper portion of the stage 2, but in themanner not shown in the figure. For this reason, it is impossible toobtain a stable detection thereof, in particular with respect to changein temperature, and disturbance due to vibration, etc.

With such the structure mentioned above, the UV light (for example, theUV laser beam) L1 emitted from the illumination light source 3, beingreflected upon the mirror 4 and penetrating through the ND filter 5 forlimiting the light amount, is expanded by the beam expander 6, to beincident upon the objective lens 14 through the coherence reducingoptical system 10, the lens 11, the beam splitter 12 and the group 13 ofpolarization elements, thereby being irradiated upon the sample (i.e.,the semiconductor wafer) 1. Namely, after being converged in thevicinity of the pupil of the objective lens 14 by means of the lens 11,the UV light L1 is given upon the sample 1 as the Koehler illumination.The reflection light from the sample 1 is detected by the image sensor20, after passing through the objective lens 13, the group 13 ofpolarization elements, the beam splitter 12, and the image-forming lens19, sequentially from the above of the sample 1 in the verticaldirection.

When being inspected, the sample 1 is always detected on the surface tobe tested, i.e., the position in the Z direction thereof, in a focusdetector system 15, through a method not shown in the figure, whilemoving the semiconductor wafer 1, as an example of the pattern to betested, at a constant speed with scanning the stage 2, therebycontrolling the stage 2 in the Z direction so that the distance betweenthe objective lens is constant. The image sensor 20 detects brightnessinformation (i.e., gradation image signal) of the pattern to be tested,which is formed on the semiconductor wafer 1.

A signal processor circuit 24 is constructed with an A/D converter 200,a gradation conversion portion 201, a video filter 215, a delay memory202, an position alignment portion 203, a local gradation conversionportion 204, a comparing portion 205, a CPU 212, an image input portion206, a scatter diagram producing portion 207, a memory means 208, adisplay means 209, an output means 210, and an input means 211, etc.

The A/D conversion portion 200 converts gradation image signal, whichcan be obtained from the image sensor 20, into digital video signal,thereby providing an output of video signal of the sample. For example,ten (10) bits data is adopted. The gradation converter 201 performs suchthe gradation conversion described in Japanese Patent Laying-Open Hei8-320294 (1996) upon the 10 bits digital video signal, which isoutputted from the A/D converter 200. Thus, the gradation converter 201treats it with the logarithm transformation, the exponentialtransformation, or the multinomial transformation, etc., therebycompensating the image, and it is so constructed that it can provide anoutput of eight (8) bits digital signal, for example.

The video filter 215 is a filter provided for removing noises beingcharacteristic to the image detected under the UV light from the image,which is gradation-converted and compensated, with high efficiency. Thedelay memory 202 is a memory portion for memorizing a reference imagesignal therein, and it memorizes the output image signal from the videofilter 215, for a one cell or a plural number of cells, or for an onetip or a plural number of tips, being repetitively formed on thesemiconductor wafer, so as to delay. Herein, the cell constitutes a unitof repetition within the tip. However, the video filter 215 may beprovided after passing the delay memory 202. The position alignmentportion 203 is a portion for detecting an amount of positional shift ordeviation between the image signal (i.e., the detected image signalobtained from the sample) 213 treated with the gradation conversion,which is outputted from the gradation converter 201, and the delayedimage signal (i.e., the reference image signal) 214 obtained from thedelay memory 202, through the normal function, thereby aligning theposition by a unit of the cell. The local gradation conversion portion204 is a portion for conducting the gradation-conversion upon both orone of the image signals, being different in the characteristic quantity(i.e., the brightness (the difference in tone), the contrast, thedifferential value, the standard deviation, the texture, etc.) of anormal portion, locally (i.e., for each predetermined area or region),so that the characteristic quantity of the said normal portion coincideswith each other locally (i.e., for each predetermined area or region).Thus, both or one of the image signals are compensated through the localgradation-conversion, so that the characteristic quantity of thedetected image signal and that of the reference image signal arecoincident with each other, with the normal portion. With doing this, ifa difference is generated between the detected image signal and thereference image signal, in the brightness, the contrast or the like, itis possible to bring them to be coincident with, through the localgradation-conversion, and therefore, without generating erroneousinformation, it is possible to detect the defects with high sensitivity,by means of a decision threshold value upon basis of the difference inthe characteristic quantity thereof.

The comparison portion 205 is a portion for comparing the detected imagesignals by themselves, which are treated with the gradation-conversionin the local gradation-conversion portion 204 locally (i.e., for eachpredetermined area or region), thereby detecting the defects or thedefect candidates by means of the decision threshold value upon basis ofthe difference in the characteristic quantity. Thus, the comparisonportion 205 compares the reference image signal, which is outputted fromthe delay memory 202 and is delayed by an amount corresponding to thecell pitch, etc., with the detected image signal.

By inputting the coordinate, such as alignment data or the like on thesemiconductor wafer 1, through the input means 211, being constructedwith, such as a keyboard, or a disc, etc., the CPU 212 produces defectinspection data upon the basis of the coordinate, such as the alignmentdata, etc., on the semiconductor wafer 1, and stores it into the memorymeans 208. This defect inspection data can be displayed on the displaymeans 209, such as a display, if necessary, and also can be outputted tothe output means 210. Further, the details of the comparison portion 205may be such, as shown in Japanese Patent Laying-Open No. Sho 61-212708(1986), for example, and may be constructed with a position alignmentcircuit for an image, a differential image detector circuit for theimage aligned in position, an anti-coincidence detector circuit fordigitizing the difference image, and a characteristic extractor circuitfor calculating out an area, a length (a projection length), or thecoordinate, etc., from the digitized output. In brief, from thecomparison process portion 205 is outputted information in relating withthe position and the sizes of the defects on the pattern to the CPU 212,therefore the defect inspection data is produced in the CPU 212.

The image input portion 206 is a portion for inputting in synchronism orin non-synchronism, for the purpose of producing scattered diagrams forboth images, which are aligned in the position by a unit of the cell inthe position alignment portion 203. The scattered diagram producingportion 207 is provided for producing the scattered diagrams, betweenthe characteristic quantity of the detected image by a unit of pixel andthe characteristic quantity of the reference image by a unit of pixel,for respective categories (i.e., the brightness (the difference intone), the contrast, the differential value, the standard deviation, thetexture), for each the predetermined area (locally), with respect to theboth images inputted in the image input portion 206, thereby fordisplaying them on the display means 209, for example.

An example of the video filter 215 will be explained. FIG. 26 shows aflow of processes. First, upon the detected image and the referenceimage inputted are conducted removal of noises (281) and improvement onimage quality (282), depending on the necessity thereof, therebyimproving the S/N ratio. For the removal of noises, various kinds offilters are prepared; therefore it is possible to select it dependingupon the target and/or the quality of noises. As an example thereof, amethod can be listed up, in which values in the vicinity thereof areused with weight. In actual, the values in the vicinity of n×m, withrespect to the pixel on which attention is paid, are multiplied with afilter coefficient(s) to be added with. In FIG. 27, it is the case wherem=n=3, and the weight of each the pixel value in the vicinity isone-eighth (⅛). The value of the attended pixel comes to be (Eq. 1).F(i,j)=B·⅛+D·⅛+F·⅛+H·⅛+E·⅛  (Eq. 1)

The size and the coefficient of the filter can be changed flexibly, byusing a lookup table thereof. As another example, there is known amedian filter. With this, taking a central value among the brightnessvalues in the vicinity where the setting is made, it is possible toremove an ill influence of a singular point. Alternatively, in otherexample is used the Gaussian function. With this, smoothing of image isconducted through the convolution; i.e., first convoluting an average 0upon the image f(x,y), and then two (2)-dimensional Gaussian function(Eq. 2) upon (Eq. 3).G(x,y)=(½πσ²)·exp(−(x ² +y ²)/2σ²)  (Eq. 2)F(x,y)=G(x,y)

f(x,y)=∫∫G(x+u,y+v)·f(x,y)dudv  (Eq. 3)

where,

means the convolution.

Also, in other example, it is possible to remove the noises generatingirregularly, by using the Fourier transform.

Next, restoration is made (282) on the image, which is deterioratedthrough the noise removal (281). As an example of this, the restorationis made by means of the Wiener filter. In this, the image is given, sothat an averaged square error between the image f(x,y) after beinginputted and the image f′(x,y) after the restoration comes to theminimal.

Further, it is checked whether there is a large difference or not, in aview between the detected image and the reference image to be comparedwith. Indexes for evaluation include the characteristic quantity (i.e.,the brightness (tone value), the contrast (the brightness value), thedispersion of brightness (the standard deviation), the frequencies ofnoise components, the texture). Then, upon the detected image and thereference image, which are aligned in the position by a unit of pixel,the characteristic quantities are calculated out (283) for therespective categories; i.e., the brightness (tone value), the contrast,the dispersion of brightness (the standard deviation), the frequenciesof noise components, the texture, etc., for each the predetermined areacorresponding thereto (for each location) In the normal portion, ifthere is local difference between the detected image and the referenceimage in any one of the characteristic quantities, then first of all,sequential image compensation (i.e., sequential gradation-conversion) isconducted, locally, so that those characteristic quantities come closeto each other. Thus, for each category, the characteristic quantities(such as, the tone value, or the brightness value, etc.) of the detectedimage and the reference image are compared with, for each areacorresponding thereto, thereby extracting the difference therebetween.For example, for each category, and for each area, the scattered diagramis produced, by depicting the brightness value, as the characteristicquantity of the detected image by a unit of pixel of, on the horizontalaxis, while the brightness value of the reference image, as thecharacteristic quantity by a unit of pixel, on the vertical axis. Then,compensation coefficients (a,b) are obtained upon the basis of anintersection point b between an inclination a of a line drawn in thearea mentioned above, by fitting the straight line thereto (i.e., alinear approximation), for example, on the scattered diagram that isproduced for each area. And, for example, compensating one of theimages, i.e., the detected image f(x,y) (i.e., fitting of the image)(285) through the compensation coefficient mentioned above, for eacharea, enables to obtain the detected image signal f′(x,y), beingcoincident with the reference image in the characteristic quantitythereof, for each area, if it is the normal portion. Namely, as a resultof the compensation, the detected image and the reference image arescattered under the condition that they are restricted onto a straightline of 45 degree in the scattered diagram, and thereby setting adecision threshold value for deciding to be the defects or the defectcandidates, with respect to the difference (the difference image)between the detected image and the reference image, by a straight linehaving a certain width to that of 45 degree. In this manner, thedecision threshold value can be obtained from the scattered diagram.f′(x,y)=a·f(x,y)+b

In this fitting of image, the Wiener filter mentioned above may beapplied between the detected image and the reference image. Also, invideo processing, if the image is at a level where the fitting of thelocal characteristic quantity is impossible, the sensitivity is lowereddown, by increasing the decision threshold value in the comparisonprocess portion 205, for extracting the defects and the defectcandidates with respect to the difference (the difference image) betweenthe detected image and the reference image, thereby suppressinggeneration of the erroneous information (286).

Further, the method for calculating the defects in the video processingportion 24 can be realized, in the details thereof, by that shown inJapanese Patent Laying-Open No. 2000-194323, for example.

Next, explanation will be given on the illumination light source 3.Although shortening is necessary, in particular, in the wavelengththereof, for achieving the high resolution, it is thought appropriate touse the laser for the light source, as a means for obtaining anillumination of high luminance within wavelength region of the UV, beingmost effective in the effect thereof. As was mentioned in the above,adopting the UV laser light as the light source brings about a largemerit. According to the present invention, there is shown a method ofusing the illumination by means of the UV laser light.

FIGS. 2( a) and 2(b) show the condition of illumination on the pupil ofthe objective lens and a visual field, when being illuminated under anordinary white light. AS in FIG. 2( a) indicates the pupil, and FS thevisual field. At the position of the pupil AS, an image 30 of the lightsource is formed, while the entire of a visual field 31 is illuminated,equally, at the position of the visual field FS.

Next, in FIGS. 3 (a) to 3(d) are shown the cases where the illuminationis obtained by means of the UV laser light source. In this case, asshown in FIG. 3( a), the light source image 32 comes to be a point atthe position of the pupil AS. The illuminated circuit pattern shown by30 on the visual field FS, as shown in FIG. 3( b), if being the patternin the cross-section thereof as shown in FIG. 3( c), comes to be animage having a detection waveform shown in FIG. 3( d). In this manner,when obtaining the image of circuit pattern while illuminating it by thelaser light, an overshoot or an undershoot, or a speckle occurs at theedge portion thereof. The reason thereof lies in a fact that σ of theillumination is small. In other words, the illumination onto the visualfield FS under the objective lens 14 is not carried out from variousangles.

Under the illumination of an ordinary white light, an illumination isperformed to have a certain size on the pupil AS, thereby illuminatingto the visual field FS from the directions having an angle rangecorresponding to the NA (i.e., the number of aperture) of the objectivelens 14. Under the coherent light (i.e., having coherency), such as, thelaser light, σ (in proportion to the size of a light source on thepupil) comes to be zero (0). This is because an image of the lightsource is a point with such the coherent light, therefore the image onthe pupil becomes a point. Of course, as shown in FIG. 4( a), though itis possible to project the light flux 34 expanded by other lens systemupon the pupil 14 a (AS) of the objective lens 14, however since the UVlaser light has the coherence, it comes to be the same result (see 35shown in FIG. 4( b)) where all the lights come out from the position ofσ=0, therefore it brings about no solution thereof.

Accordingly, there is a necessity of a means for lowering the coherenceof the UV laser light. For the purpose of lowering the coherence, it issufficient to reduce either one of the time coherence or the spatialcoherence thereof.

Then, according to the present invention, as a function of alightscanning mechanism (or a light scanning system) for scanning on thepupil, which constructs a light modulator as the coherence reducingoptical system 10, it is proposed that illumination 40 is made upon thevisual field shown in FIG. 5( b) by scanning, for example, first byilluminating upon the position 36 within the FIG. 5( a), and then uponthe position 32, and the upon the position 33 . . . , while forming theimage of light source upon the pupil 14 a of the objective lens 14 inthe inspecting apparatus. And, as shown in FIG. 5( c), the scanning 41may be made in a swirl-like manner on the pupil 14 a. Also, as shown inFIG. 5( d), the scanning 42 may be made in two (2) -dimensional manner.During this, images of the speckle, the overshoot and the undershoot maybe obtained at the respective positions, however they have no coherencedue to the difference in the time instance when each being obtained.Accordingly, adding those images upon the image sensor 20 enablesobtaining the image being same to that formed with the incoherent lightsource. For achieving the addition thereupon, suitably, the image sensor20 has a pixel size from about 0.05 μm to about 0.3 μm, being convertedon the sample (on the visual field), and is a detector of accumulationor storage type (in more details, the TDI sensor), such as a CCD. Thus,such an image sensor of accumulation or storage type, it can beconsidered that a linear sensor is applied to.

As shown in FIG. 6, if illumination is made all over surface of thevisual field to the linear sensor 51, only the illumination at an area52 can contribute to the detection, but an area 50 other than that hasno contribution to the detection, which occupies a large part of anoptical power. Then, for the purpose of improving the luminance, it ispreferable to perform a line-like (or slit-like) illumination onto thelinear sensor 51 within the area 53, as shown in FIG. 7. According tothe present invention, with such the image sensor 20, it is constructedby using a sensor of time delay integration type among the CCD sensors,i.e., the TDI (Time Delay Integration) type. In case of the TDI sensor,N stages (from several tens to 256 stages) of light receiving portionsare aligned on the visual field in a shorter direction thereof, while aplural number of the stages are aligned in the longer direction, therebybuilding up the linear sensor.

FIGS. 8( a) and 8(b) show the structure of the laser beam source. Thelaser beam source 3 is fixed on a plate 102. A plate 101 is fixed withaligning to an optical base 100. Position alignment is made, forexample, by fixing with using a pin 103 fixed on the optical base 100 asa guide. Herein, it is assumed that the pin 103 is adjusted with respectto an optical axis of the optical system. The plate 102 is fixed on theplate 101. The laser beam source 3 happens to be replaced with new one,due to the lifetime of a laser oscillator. When the laser beam source 3is replaced, there is a probability that the stoppage time of theapparatus comes to be long if adjusting the optical axis of the opticalsystem. For this reason, preferably, the laser beam source 3 iscompleted in adjustment of the optical axis thereof before it is mountedfor replacement, so as to obtain a desired performance at the lowest.

FIGS. 9( a) and 9(b) show an example of a jig for adjustment of opticalaxis. An optical axis adjustment base 104 is fixed by the pin 103 on theposition being same to that of the optical base 100. Targets 105 and 106are same in the height, and are fixed in parallel relationship with theposition of the pin 103, while each being opened with a pinhole 107 forpassing the laser beam therethrough. The distance between the targets105 and 106 has a sufficient length for adjusting the laser beam source3. In this structure, the plate 101 is fixed onto the optical adjustmentbase 104. The laser beam source 3 is provisionally fixed on the plate102 in advance. Then, the plate 102 is mounted on the plate 101, therebyemitting the laser beam therefrom. The light flux L is adjusted in theright-hand and the left-hand side directions (i.e., in the horizontaldirection) by means of the plate 102, so that it can pass through thepinholes 107 of the targets 105 and 106, while by the laser beam source3 itself in the gate direction (i.e., in the vertical direction). Afterthe adjustment, the plate 102 and the laser beam source 3 are fixed, andfurther the plate 102 is fixed onto the plate 101. In this manner, thelight flux of the laser beam source 3 is adjusted upon the basis of thepin 103. Thereafter, replacing with the laser beam source 3 fixed on theplate 101 onto the optical base 100 brings about the coincidence of theoptical axis thereof.

Next, explanation will be given on the ND filter (a light amountadjustment optical system) for restricting (adjusting) a light amount,by referring to FIG. 10. The light flux L1 from the laser beam source 3is irradiated at the maximum output, for the stability of laser. Forthis reason, it is necessary to restrict the light amount reaching up tothe image sensor 20. Thus, a ND filter 5 is inserted in the opticalpath. As such the ND filter 5 is used a filter changing the permeabilitydepending upon the angle, as shown in FIG. 11, for example. The NDfilter can be rotated through a method, but not shown in the figure;thus, includes a light amount adjustment system for fixing at apredetermined angle. Also, the ND filter 5 is inclined by an angle α tothe light flux L2. It is sufficient that the angle α is set at such anangle that the light flux R reflected from the ND filter 5 will notdirectly turn back to a laser emission opening of the laser beam source3. Namely, it is for the purpose of protection from a phenomenon, suchas, interference occurs within the oscillator of the laser beam source3, thereby bringing the laser output into an unstable condition. As wasexplained in the above, the light amount adjustment optical system isconstructed with the ND filter 5, which is able to lower the lightamount, and the optical amount setting system, which can set thepenetrating light at an arbitrary amount by changing the inclinationangle α in optical axis of the ND filter portion with respect to theoptical axis L2.

Next, explanation will be given on the optical path exchanger system(i.e., illumination area exchanger means) 7. FIGS. 12( a) to 12(d) showthe structure of the optical path exchanger system 7. Within the opticalaxis 60 is inserted a homogenizer (i.e., a slit-like light flux opticalsystem) 74, for the purpose of illuminating the sample 1 by theslit-like light flux when inspecting. And, it is constructed withmirrors 63, 64, 65 and 66, and a lens 67, which are fixed on a base 62,for illuminating upon an entire detection area 72 of the detector whenadjusting the inclination. The base 62 is constructed, being movableinto the side of the optical path 60, but through a manner not shown inthe figure, thereby being constructed to exchange the optical path wheninspecting and when adjusting the inclination.

First, explanation will be given when inspecting. As was mentionedpreviously, because of use of the linear sensor, it is effective toperform a rectangular illumination 71 (i.e., illumination with using aslit-like light flux), irradiating all over the surface in the pixeldirection while focusing or condensing onto the sizes of the sensoropening in the scanning direction, within the range of illumination wheninspecting. For this reason, for forming a slit-like spot light (i.e.,the light flux being focused or converged in the width direction of thelinear sensor, such as the TDI sensor, etc.), the homogenizer 74 isinserted after emission of the light from the beam expander 6, as shownin FIG. 12( a), thereby achieving the rectangular illumination. FIG. 13shows the structure of the homogenizer 74. The homogenizer (i.e., theslit-like light flux optical system) 74 is used, which is constructed byaligning a plural number of rectangular lens arrays 70 in the verticaland the horizontal directions. Thus, the homogenizer 74 is constructedby aligning the rectangular lens arrays 70 which, as shown, have arectangular cross-sectional configuration, being different in the pitchin the vertical direction and the horizontal direction. With this, onthe surface of a sample can be obtained the rectangular illumination (bythe slit-like light flux) 71 (53). FIG. 12( a) shows the arrangementwhen achieving the rectangular illumination. FIG. 12( c) shows a rangeof illumination upon the surface of the sample 1. Thus, the illuminationcan be obtained within the range 71 (53) covering the image sensor, inthe visual field 72 of the objective lens 14. However, the homogenizer74 forms a large number of points of imaginary light source to the laserbeam that is expanded in the beam diameter. Accordingly, as shown inFIG. 5, the large number of the points of imaginary light source arescanned at the same time upon the pupil 14 a, in two (2) dimensionalmanner, thereby lowering the coherency.

By the way, the sample 1 is shifted onto the stage 2 by a method notshown in the figure. The sample 1 must be positioned, so that thepatterns formed on the sample 1 are correctly aligned or fitted to theinspection direction of the apparatus, i.e., the scanning direction, forreducing the detection errors. For that purpose, it is necessary tocompensate an inclination of the sample 1. In the present embodiment, amethod will be explained, in which the inclination compensation iscarried out by using a detector 18, which is provided in the opticalpath. First, by using tips at both ends of the sample 1, alignment marksprovided within the tips, but not shown in the figure, are detected, soas to calculate out the inclination of the sample 1. Since theinclination of the sample 1 is unknown, it is necessary to enlarge thedetection range of the detector 18, by making the optic magnificationsmaller than that for use in the inspection. As was mentionedpreviously, since the illumination area for use in the inspection isrectangular, the target falls down into a condition where noillumination is made in the direction perpendicular to the scanningdirection when it is detected by the detector of wide visual field. Forthis reason, it is necessary to make illumination all over the detectionarea of the detector.

Explanation will be given on the illumination when compensating theinclination. In FIG. 12( b) is shown the arrangement for achieving theillumination when compensating the inclination. The light flux 60 isbent by means of the mirrors 63, 64, 65 and 66. Since the light flux 68comes to an ordinary illumination light flux, by the function of thelens 67 provided within the optical path, therefore the illuminationarea on the objective lens 14 is circle in the shape thereof. FIG. 12(d) shows illumination area on the surface of the sample 1. Theillumination is made all over the surface within the visual view 72 ofthe objective lens 14, therefore it is possible to cover the detectionarea 73 of the detector 18, fully.

Next, explanation will be given on the aperture diaphragm system. FIG.14( a) shows an example of the aperture diaphragm. The aperturediaphragm 8 is able to change a system, through which the light fluxpasses in the manner not shown in the figure. The position, at which theaperture diaphragm 8 is disposed, is that being conjugate to the pupilposition of the objective lens 14. Depending on the surface shape of thesample as the target, it is possible to fit with the surface conditionby the aperture diaphragm 8 being made changeable. Also, it is possibleto make the aperture diaphragm 8 in a ring-like shape. FIG. 14( b) showsthe shape of the aperture diaphragm 8 a when achieving a ringillumination. Changing of the ring shape in various kinds by a manner,but not shown in the figure, enables the detection with higherresolution.

Next, explanation will be given on the coherency reduction opticalsystem 10. In the present embodiment, the reduction of coherency isachieved by a method of providing a diffuser panel within the laseroptical path. FIG. 15 shows the structure of the coherency reductionoptical system 10. An image of the UV laser beam is formed upon thepupil 14 a of the objective lens 14 through the lenses 90 and 91. Withinthe optical path, a diffuser panel 92 is inserted, which moves crossingover the optical axis. The diffuser plate 92 can be rotated, forexample, by means of a motor 93, so as to move crossing over the opticalaxis. The diffuser plate 92 is positioned in the vicinity of theconjugate point to the sample 1. The shape of the diffuser 92 is shownin FIGS. 16 (a) to 16(c). FIG. 16( a) shows the front view, and FIG. 16(b) a detailed view of the diffusion surface. FIG. 16( c) shows thecross-section X-X in FIG. 16( a). Observing from the surface,preferably, the diffuser 92 is formed by disposing or aligning particles94, 95 and 96, each having a size of about 0.1 mm in the particlediameter and being formed in a polygon or a circle in shape. Also, thecross-section is preferable to random shapes depending on the particlediameter, even in an amount of concave and convex. Rotation of thisdiffuser plate 92 with high speed enables to negate the opticalcoherency completely. As a manner for rotating with high speed, applyingan air turbine motor as the motor 93 enables the rotation speed ofseveral kHz. As is shown in FIG. 15, there is a possibility the outerdiameter of the motor 93 interferes with the lens 91, therefore thediffuser plate 92 must be made large. For this reason, a condition canbe considered, where a desired rotation speed cannot be obtained, due toeccentricity, inertia, etc., when the diffuser plate rotates. In FIG.17, there is shown an embodiment, in which the diffuser plate 92 has thesize, being necessary and minimal. Introduction of the lenses 90 and 91are same to those in FIG. 15 mentioned above. The diffuser plate 92 isdisposed, inclining with an angle to the optical axis. The lens 91 wasalready positioned, by taking a gap in the optical axis due to theinclination into the consideration. With this, the interference betweenthe motor 93 and the lens 93 can be prohibited, and therefore, thediffuser plate 92 can be manufactured to have the necessary and minimalouter diameter.

Also, similar effect can be obtained by provision of a rotational phaseplate in the place of the diffuser plate 92 mentioned above. FIGS. 18(a) to 18(c) show the structure of the rotational phase plate. Thus, FIG.18( a) is a view for showing the front view, FIG. 18( b) for sowing thedetails, and FIG. 18( c) a view for showing the cross-section X-X inFIG. 18( a). The rotational phase plate has such the thickness that nochange occurs in phase at the position 98. For example, it ismanufactured by shifting phase difference, ½λ, ¼λ and ¾λ . . . , in thestep difference. A large number of those step differences, beingdifferent in depth, are treated thereon at random. This rotational phaseplate is fixed onto the motor 92 in the place of the diffuser plate 92,as shown in FIG. 17, and rotation thereof enables to change the phase ofthe laser beam depending upon the depth of each of the steps, therebythe coherency of the laser can be lowered.

Next, the structure of the optical path exchanger mechanism will beshown. FIG. 19 shows the optical path exchanger mechanism. The opticalpath exchanger mechanism is provided for exchanging the optical pathbetween the image sensor 20 and the detector 22. The mirror 21 can beinserted into the optical path by a manner, but not shown in the figure.The detector 22 is fixed at the position, being conjugate with theimage-forming position of the image sensor 20, under the condition wherethe mirror 21 is inserted into the optical path. When inspecting, themirror 21 is in a turnout or escaped condition, and it is shifted intothe optical path when observing the inspection result, via a manner notshown in the figure, thereby enabling the observation of the sample 1 bymeans of the detector 22. And, the detector 22 is attached under thecondition of inclining to the optical axis. The detector 22 is providedwith a cover glass in a front thereof, in general, thereby protectingthe sensor. The laser beams cause multi-interferences when beingincident upon the surface and the reverse surface of the glass,therefore interference patterns appear on an observation screen in thedetector. For this reason, the detector 22 is adjusted at angles α1 andα2, so that no interference occurs, to be fixed, thereby being able toprotect from occurring the interference patterns thereon. Further, thedetector 18 is also inclined in the same manner.

However, the image-formation lens 19 is used, by changing it to have themagnification corresponding to the pixel size. Thus, when the pixel sizediffers, not the objective lens 14, but the image-formation lens 19 isexchange. Further, the image-forming positions of the image-formationlenses 19 a, 19 b and 19 c, having the respective magnifications, areset at the same position, irrespective of the difference inmagnification thereof. Therefore, there is no necessity to change theposition of the sensor 20 if the magnification is different, therebyenabling a stable detection. Also, the magnification is determinedthrough the focal distance of the objective lens 14 and those of theimage-formation lenses 19 a, 19 b and 19 c, and the pixel size isdetermined by the size of aperture of the image sensor 20. However, dueto errors occurring in manufacturing the objective lens 14 and theimage-formation lenses 19 a, 19 b and 19 c, as well as in installthereof, there is a probability that the magnification differs for eachlot. Therefore, there will occur a problem that the detectionsensitivity differs for each lot for the optical system, thus, for eachapparatus. For this reason, each of those image-formation lenses 19 a,19 b and 19 c has a mechanism for making the focal distance thereofbeing variable.

FIG. 20 shows the cross-section view of the image-formation lens. Theimage-formation lens 19 is constructed by combining plural pieces oflenses 501, 502, 503 and 504 within a lens-barrel or -tube 500. Thedesigning of those image-formation lenses are conducted, so that thefocal distance thereof can be changed, for example, through shifting aone piece of those lenses into the optical thereof. In a case where theshifting of the lens 503, which is shown in FIG. 20, can change thefocal distance, the lens holder 505 is so constructed that the lens 503can be shifted from an outside of the lens barrel 500. Shifting this,with a manner not shown in the figure, causes a change in the focalposition (or the focal distance), while the focal distance of theobjective lens 14 is constant; therefore it is possible to cause achange in the magnification. Further, of course, a similar effect can beobtained by applying a zoom lens to the image-formation lens for makingthe magnification variable.

Next, explanation will be given on an example of the TDI sensor, beingable to detect the UV light, in particular the DUV light in this manner.FIG. 21 shows a surface reflection type sensor. In case of using a DUVlaser beam source as the illumination light source 3, it is necessary toapply an image sensor having sensitivity to the DUV light. In an imagesensor 200 of surface irradiation type, incident light 150 enters into aCCD 155, penetrating through a cover glass 151 and passing through agate 154, thereby being attenuated with the short wavelength; thereforeit has almost no sensitivity to the wavelength less than 400 nm, and isunable to detect the DUV light effectively. Then, a method is alreadyknown, for detecting the DUV light by means of the image sensor havingthe sensitivity only to the visible lights, wherein an organic thin-filmcoating 152 is treated on the cover glass 151, so as to emit visiblelight responding to an incident DUV light thereupon.

FIG. 22 shows an image sensor of such organic thin-film coating type. Inthe organic thin-film coating type image sensor 201, the organicthin-film coating 152, receiving the penetrating light of the incidentlights, emits fluorescence lights from the organic thin-film coatingsurface 152, therefore it can detect the DUV light by means of thesurface irradiation type image sensor having the sensitivity to thevisible lights.

FIG. 23 shows the spectral characteristics or properties. A spectralcharacteristic 156 depicts that of an ordinary surface irradiation typeimage sensor 200. It has no sensitivity to the lights having wavelengthshorter than 400 nm. A spectral characteristic 157 depicts that of theimage sensor 201 of organic thin-film coating type. It is added with thesensitivity to the lights having wavelength shorter than 400 nm.

For further improving the sensitivity to the DUV light, it is preferableto adopt an image sensor of reverse-surface irradiation type. FIG. 24shows the structure of the reverse-surface irradiation type imagesensor. The incident light 150 penetrates through the cover glass 151,to be incident upon a reverse-side where no gate structure is built up.For this reason, it shows a spectral characteristic 161, as shown inFIG. 23, because of no passage through the gate 154, therefore it isadvantageous for the illumination with the short wavelength lights notreaching to 200 nm; i.e., being high in the quantum efficiency (forexample, being 30% or more), being wide in the dynamic range (forexample, being 3,000 or more), and being sensitive to the wavelengthless than 400 nm. In case of using such the image sensor, it is possibleto deal with by means of only one image sensor even if using severalwavelengths for the illumination. Also, using the TDI (Time DelayIntegration) type of the image sensor 201 enables to increase thesensitivity. Further, letting to have the characteristic ofanti-blooming enables to dissolve the problem that electric charge flowsout into peripheral pixels when obtaining the detection of light beingmuch more than necessary in an amount.

Next, explanation will be given on the installation or attachment of theimage sensor 20. FIG. 25 shows a method for attaching the sensor. As wasmentioned previously, since it includes the cover glass, the imagesensor 20 has a possibility that the interference pattern is generatedupon the glass surface. Inclination of the sensor 20 by an angle θ inthe direction of the number of stages thereof enables to prevent theinterference pattern from generating due to the interference of thelaser beam, while generating the deviation in the focus in the directionof pixels.

Further, in addition to the high resolution by means of the UV light, anexplanation will be given on a method for improving the patterncontrast, through controlling the polarizing elements group 13, as wasmentioned previously. For the purpose of increasing the patterncontrast, by paying attention to the fact that the polarizationcondition of the UV light can be controlled freely upon the basis of thecontrol of the polarizing elements group 13, the direction ofpolarization of the illumination light, i.e., the elliptical ratio iscontrolled, thereby enabling the detection of a part of polarized lightelements of the detected light by means of the image sensor 20. Ascharacteristics of the illumination by the UV light, there are factsthat it has a single wavelength, and that it is a linearly polarized orplane polarized light. For this reason, it is possible to control thepolarization condition, with high efficiency, by means of the polarizingelements group 13, including a ½ wavelength plate and a ¼ wavelengthplate provided within the optical path. The control can be achieved byrotating the ½ wavelength plate and/or the ¼ wavelength plate. Since thepattern contrast changes greatly depending upon the polarizationcondition of illumination, performances of the optical system can beimprove, by bringing the polarization condition to be controllable(i.e., positioning by rotation of the wavelength plate(s)). In moredetails, the linearly polarized light can be controlled in the directionby means of the ½ wavelength plate, while the elliptical ratio by meansof the ¼ wavelength plate. With this, it is possible to obtain animprovement of the detection sensitivity. With combination of those, itis also possible to achieve the horizontal Nicol and the vertical Nical.Of course, it is also possible to achieve the circularly polarizedlight. However, those do not depend upon the illumination wavelengthitself. Also, if such an idea mentioned above can be established, thestructure may be in any kind for achieving it. Of course, a spatialfilter may be disposed at the position being conjugate with the pupil ofthe objective lens 14, thereby attenuating the 0^(th) dimensional light(or, it may be possible to guide the scattered light from the foreignmatter into the image sensor, through blocking the diffracted light fromthe pattern by means of the spatial filter). However, controlling thepolarized light enables more effective extraction of the diffractedlight therefrom. According to experiments made by the present inventors,it is clear that the contrast can be improved by about 20%-300%. Also,an analyzer (not shown in the figure) may be positioned between thesample 1 and the image sensor 20, to be controlled on rotation thereof,thereby detecting the image of the sample from the reflection lightwhile controlling the polarization condition in the detection opticalsystem.

As was explained in the above, using the DUV light, such as that havingwavelength of 266 nm, 248 nm or 192 nm, enables the detection of defectson the device, being under less than 0.07 μm rule. Also, it can beapplied to the inspection of Cu damascene, as a target to be inspected,Further, the inspection can be made even onto a portion where no patternis formed on the target to be inspected, since no erroneous informationis produced when comparing between the detected image and the referenceimage because of no generation of speckles.

However, with the UV light less than 365 nm in wavelength, to be used asthe illumination light, since it has high optical energy, contaminants,such as of organic material or the like, are decomposes or react upondue to the energy thereof when the UV light is irradiated upon theoptical elements, thereby attaching or adhering upon the surfacethereof. For this reason, with provision of a means for discharging aircompellingly upon the surface of the optical system by a manner notshown in the figure, and/or a means for puffing air compulsivelythereupon, it is possible to prevent the optical parts fromdeterioration thereof.

Moreover, in the present embodiment, the explanation was given only onthe structure of the light-field optical system, however it is alsopossible to obtain a similar effect if applying the structure of aco-focal microscope into the detection optical system.

According to the present invention mentioned in the above, it ispossible to obtain a UV or DUV illumination of high brightness, therebyenabling a pick-up of image with high resolution in short time-period,and as a result, it is possible to obtain an inspection apparatus withhigh speed and high sensitivity. The defects on patterns detected areoutputted with information of the positions and sizes thereof. Inparticular, the target (the sample) 1 to be inspected mentioned aboveincludes the damascene, of such as Cu, etc., being formed by buryingconductive metal, such as Cu, etc., into openings and/or grooves for via(or contac) -holes and/or wirings formed on the insulator film, such asof SiO₂, and thereafter removing excess portion deposited or accumulatedthrough polishing by means of CMP, etc. Accordingly, the inspectingmethod and the apparatus thereof, according to the present invention,can be applied to the damascene of, such as Cu, etc. Also, theinspecting method and the apparatus thereof, according to the presentinvention, in particular using the DUV light (the light havingwavelength of 266 nm, 248 nm, or 193 nm), can be applied veryeffectively, to the device under the designing rule of 0.07 μm, since itcan detects super microscopic or minute defects less than 0.07 μm insize.

Also, according to the present invention, in the method for inspectingthe defects on patterns formed on the sample, the UV laser beam isirradiated upon the sample surface, which is lowered in the coherencythereof, and then the image or video signal is processed, being obtainedvia image pick-up upon the surface of the sample, upon which this UVlaser beam is irradiated, therefore it is possible to detect the defectsless than 100 nm on the sample, and thereby to obtain informationrelating to the positions on the sample about the detected defects lessthan 100 nm.

And also, according to the present invention, the defects less than 100nm can be detected, on patterns formed on the wafer having a diameter of200 mm, with throughput of three (3) pieces per one (1) hour.

And further, according to the present invention, it is possible toobtain an effect that an image can be obtained with much highersensitivity and higher speed, being equal or superior to that obtainedunder the ordinary discharge tube illumination, by means of the laserbeam source, under illumination of short-wavelength necessary for highresolution, and further being able to achieve the and being advantageousfor an actual practice thereof, thereby enabling the detection ofmicroscopic defects with high sensitivity.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics or features thereof. Thepresent embodiment is therefore to be considered in all aspects asillustrative and not restrictive, the scope of the present inventionbeing indicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. An apparatus for inspecting pattern defects, comprising: a lightsource for emitting an ultraviolet light; a light beam shape switchingunit for switching a shape of the ultraviolet light; an illuminationsystem for irradiating the ultraviolet light onto a sample; animage-former for forming an image of reflection light reflected from thesample by the irradiation of the ultraviolet light from the illuminationsystem; a detector which includes a time delay integration image sensorfor receiving the image of the reflection light and for converting itinto a detected image signal; a monitor which monitors the image formedby the image-former; and an image processor for detecting defects onpatterns formed on the sample in accordance with the detected imagesignal; wherein the light beam shape switching unit switches the shapeof the ultraviolet light to change an illumination area on the sampleirradiated by the ultraviolet light to a slit illumination area on thesample which is longer in one direction on the sample when receiving theimage detected by the detector and to a wide illumination area on thesample which is larger than the slit area on the sample when monitoringthe image by the monitor.
 2. The apparatus according to claim 1, whereinthe light source includes a laser.
 3. The apparatus according to claim1, wherein the illumination system includes a polarizer for irradiatingthe sample with a polarized ultraviolet light.
 4. The apparatusaccording to claim 1, wherein the image-former includes an analyzer toadjust a polarization state of the reflection light.
 5. The apparatusaccording to claim 1, wherein the switching unit switches the shape ofthe ultraviolet light to irradiate the illumination area on sample bycontrolling movement of at least one member within an irradiation pathof the ultraviolet light to the sample so as to irradiate the slitillumination area longer in one direction on the sample when receivingthe image detected by the detector and to irradiate the sample in thewide illumination area larger than the slit illumination area whenmonitoring the image by the monitor.
 6. The apparatus according to claim5, wherein the switching unit controls movement of the at least onemember so as to irradiate the sample with the wide area which is arectangular area larger than the slit area when monitoring the imagewith the monitor.
 7. The apparatus according to claim 6, wherein the atleast one member is a homogenizer.
 8. The apparatus according to claim6, wherein the switching unit controls movement of the at least onemember so as to irradiate the sample with the wide area which is arectangular area larger than the slit area when monitoring the imagewith the monitor.
 9. The apparatus according to claim 7, wherein the atleast one member is a homogenizer.
 10. The apparatus according to claim1, wherein the light beam shaped switching unit changes the illuminationarea on the sample to the slit area when receiving the image detected bythe detector including the time delay integration sensor, and switchesto the wide illumination area on the sample when monitoring the image bythe monitor.
 11. An apparatus for inspecting pattern defects;comprising: a light source for emitting an ultraviolet light; a lightbeam switching unit for switching the ultraviolet light; an illuminationsystem for irradiating the ultraviolet light onto a sample; animage-former for forming an image of the sample with a light reflectedfrom the sample by the irradiation of the ultraviolet light; a monitorwhich monitors the image formed by the image-former; a detector whichdetects the image formed by the image-forming with a time delayintegration image sensor and outputting an image signal; and an imageprocessor for detecting defects on patterns formed on the sample byprocessing the image signal outputted from the detector; wherein thelight beam switching unit switches an illumination area on the samplethrough the illumination system in accordance with detection of theimage by the detector and in accordance with monitoring of the image bythe monitor.
 12. The apparatus according to claim 11, wherein the lightsource includes a laser.
 13. The apparatus according to claim 11,wherein the illumination system includes a polarizer for irradiating thesample with a polarized ultraviolet light.
 14. The apparatus accordingto claim 11, wherein the image-former include an analyzer to adjust apolarization stage of the reflection light.
 15. The apparatus accordingto claim 11, wherein the switching unit switches the shape of theultraviolet light to irradiate the illumination area on the sample bycontrolling movement of at least one member within an irradiation pathof the ultraviolet light to the sample so as to irradiate a slitillumination area longer in one direction on the sample when detectingthe image by the detector and to irradiate the sample in a wideillumination area larger than the slit illumination area when monitoringthe image by the monitor.
 16. The apparatus according to claim 11,wherein the light beam switching unit switches the illumination area onthe sample so as to concentrate a density of the ultraviolet lightirradiating the sample in a slit illumination area longer in onedirection on the sample when receiving the image detected by thedetector and switches the illuminating area on the sample to a wideillumination area larger than the slit illumination area so as todiffuse the density of the ultraviolet light when monitoring the imageby the monitor.
 17. A method for inspecting pattern defects, comprisingthe steps of: illuminating a sample with an ultraviolet light; formingan image of the sample with a light reflected from the sampleilluminated by the ultraviolet light; detecting the image formed by thelight reflected from the sample with a time delay integration sensor andoutputting an image signal; monitoring the image formed by the lightreflected from the sample; and processing the image signal output fromthe time delay integration sensor and detecting defects on patternsformed on the sample; wherein in the step of illuminating the sample, anillumination area on the sample is switched in accordance with detectionof the image with the time delay integration sensor and in accordancewith the monitoring of the image; and wherein in the step ofilluminating the sample, the illumination area is switched to be a slitillumination area longer in one direction on the sample when detectingthe image with the time delay integration sensor and to be a wideillumination area which is larger than the slit illumination area on thesample when monitoring the image.
 18. The method according to claim 17,wherein in the step of illuminating, the ultraviolet light is a laser.19. The method according to claim 17, wherein in the step ofilluminating, the ultraviolet light is a polarized light.
 20. The methodaccording to claim 17, wherein in the step of detecting the image, thelight reflected from the sample to form the image is adjusted in apolarization state.
 21. The method according to claim 17, wherein in thestep of illuminating the sample, the illumination area is switched to bea slit illumination area longer in one direction on the sample whendetecting the image with the time delay integration sensor and to be awide illumination area which is larger than the slit illumination areaon the sample when monitoring the image.
 22. The method according toclaim 17, wherein the illumination area on the sample is switched bycontrolling movement of at least one member within an irradiation pathof the ultraviolet light to the sample.